docs/images/after/remove-unused-defs.svg

<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="200" height="100">
  <defs>
    <circle id="circle1" fill="url(#rg1)"
            cx="50" cy="50" r="50"/>
    <radialGradient id="rg1">
      <stop offset="0" stop-color="yellow"/>
      <stop offset="1" stop-color="green"/>
    </radialGradient>
    </defs>
  <use xlink:href="#circle1"/>
</svg>